1. Field of Invention
The present invention relates to a tape measure and, more particularly, to a tape measure including a tape with maximum standout length for allowing smooth reeling in of the tape.
2. Related Prior Art
There are various tape measures. A tape measure includes a tape wound on a reel biased by a coil spring. The tape includes a concave-convex shape in a cross-sectional view taken along a line perpendicular to the length thereof. The concave-convex shape includes two lateral sections and a middle section extending between the lateral sections. The middle section includes a curvature radius while both of the lateral sections include a common curvature radius. Two concave-convex shapes are disclosed in U.S. Pat. No. 4,429,462. In the first concave-convex shape, the curvature radius of the middle section is identical to that of the lateral sections, i.e., the concave-convex shape includes a single section. In the second concave-convex shape, the curvature radius of the lateral sections is indefinite, i.e., the lateral sections are flat. Another concave-convex shape is disclosed in U.S. Pat. No. 6,324,769. In this concave-convex shape, the curvature radius of the middle section is not larger than that of the lateral sections while the curvature radius of the lateral sections is definite. Almost all of the tapes of the tape measures include these concave-convex shapes.
As known in the art, the shorter the curvature radii are (that is, the greater the curvatures are), the deeper the concave-convex shapes are, and the more rigid the tapes are, and the larger the standout length is, i.e., the longer the tapes extend before they collapse because of their own weight. However, the greater the curvatures are, the more difficult it is to flatten the tapes when they are reeled in. When the curvature reaches a certain point, the tapes could be damaged because the strength of the tapes could not stand the stress loaded in the tapes when they are flattened. This has been discussed in U.S. Pat. No. 4,429,462. A relation has been given between the blade width and standout length of a so-called commercially available tape as follows:
TABLE 1BLADE WIDTH, INCHESSTANDOUT LENGTH, INCHES¼12-16½35-43¾55-73186-97
As listed in TABLE 1, there should be a upper limit in the standout length for a given width of a tape.
Tapes that are more than 1 inch wide have gotten considerable attention, since wider tapes include larger standout length. That is, users can measure longer, wider and taller objects accurately without having to resort to other manners for retaining the tapes substantially straight along their length. Wide tapes are preferred also, because they can carry large numerals that can clearly be read.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.